Hello and welcome (coming from a fellow newbie to TWCL!)
Conventional advice normally dictates not to go with your first idea, but I'm having a blast with mine so far. But instead of trying side stories etc first, I let it marinate over 2 years and continually updated/reflected on it. Be unflinching in your self-criticism when questioning your story's internal logic and plotholes but not too harsh on yourself. You want your story to be the best it can be. And by the same token, if something's not working, don't be afraid to scrap it or put it aside and come back to it later when you're more experienced. Everyone's finished story is vastly different to their initial synopses.
As with fiction writing, sound advice is to read/watch what you want to make. I love shonen anime/manga so I watch/read/am inspired by my favourite series. Not only in character/storytelling tropes, but also in terms of shot composition etc.
If you need to brush up on your art fundamentals do it as soon as possible but have fun with it and don't get too bogged down in the drills etc unless you really enjoy that stuff. Noodle around, play to your strengths, work on weaknesses and get as much feedback from laymen and hobbyists as you can.
In terms of webcomicing, definitely take the time to work on your website. The more thorough you are the better. I have stumbled upon countless webcomics where the site is either bare-bones, formatted poorly, suffers from garish design, or there's no just care put into it. If you have a dream project put everything you have into it. Make that cast page, make sure all those links are functional. I put my stuff up for a month before official launch just to ensure the site was working fine and am still refining it/working on it now.
I'm no expert to this as this is my first comic as well, but this advice hasn't steered me wrong yet. Good luck with all your endeavours and ask if you need help![/b]